1. Technical Field
The present invention relates to a line head which scans a light beam across a surface-to-be-scanned and an image forming apparatus using such a line head.
2. Related Art
Proposed as line heads for scanning a light beam across a surface-to-be-scanned include for instance a line head of an image apparatus described in JP-A-6-297767 which uses luminous element groups (referred to as the “light emitting diode arrays” in this publication) obtained by arranging plural LEDs (light emitting diodes), which are luminous elements, on a base plate which is a substrate.
In the image apparatus described in JP-A-6-297767, a resin lens plate which includes a plurality of imaging lenses such that each imaging lens corresponds to each one of the plural luminous element groups is opposed via a spacer to the luminous element groups. The linear expansion coefficients of the base plate, the lens plate and the spacer are within the range of −2 through 3×10−6/° C. at a temperature ranging between −30° C. and 100° C., which suppresses displacement due to a temperature change of the base plate, the lens plate and the spacer relative to each other.
Meanwhile, Japanese Patent No. 2510423 discloses a structure that light shielding plates and the like which are light shielding members surround a space between LED array chip and the imaging lenses like a box to thereby discourage “crosstalk”, the phenomenon that light from the LED array chip leaks to the neighboring space or to the outside and deteriorates the printing quality.
To be more specific, plural light guiding holes are formed in the light shielding parts such that each light guiding hole corresponds to each one of the plural luminous element groups. The light guiding holes extend from the associated luminous element groups toward the imaging lenses which correspond to the luminous element groups. Light beams emitted from the luminous element groups, passing through the light guiding holes to which the luminous element groups correspond, impinge upon the imaging lenses which correspond to the luminous element groups. In other words, of the light beams emitted from the luminous element groups, only those passing through the light guiding holes are incident upon the imaging lenses which correspond to the luminous element groups. The light beams impinging upon the imaging lenses are imaged on a surface-to-be-scanned, whereby spots are formed on the surface-to-be-scanned.
Also proposed as a line head of this type is a line head which uses luminous element groups (referred to as the “luminous element arrays” in this publication) obtained by arranging plural luminous elements as described in JP-A-2000-158705 for example. In the line head according to this publication, the plural luminous element groups are arranged side by side and plural imaging lenses are disposed so that they are opposed to the plural luminous element groups on the one-to-one correspondence. Light beams emitted from the luminous elements of the luminous element groups are imaged by the imaging lenses which are opposed to the plural luminous element groups, whereby spots are formed on a surface-to-be-scanned.